Conventional valves for automatically discharging condensate from compressed air systems which include the float type, the air pilot type, and the motor type, among which the motor type is the most reliable in discharging the condensate. The conventional condensate discharging apparatus of the motor type has a fixed or variable condensate discharging cycle or discharging period. In the fixed period type, the discharging period must be selected so that the largest probable quantity of the accumulated condensate will be discharged. Accordingly, in the winter season when the quantity of condensate is the smallest, the quantity of purge air becomes relatively large so that the air loss becomes unduly large and, in a small air pressure system, a drop in pressure is caused thereby.
In the variable type which is adjustable according to the quantity of the condensate produced, the discharging period is usually set somewhat longer so as to discharge the condensate surely and, accordingly, the apparatus has a complicated construction.
Further, absence of an indicator to check the operating condition of the apparatus from outside is a cause of inconvenience.